Elevated operating speed of central processor units of electronic computers has demanded corresponding speed-up of high speed printing machines which output unit of such computer and various systems have been developed to meet such demand.
A typical example of such known systems is the one in which ink is supplied to the nozzle under extremely low pressure so that ink is bulged out half-spherically from the nozzle end, then ink is drawn out in the form of droplets by providing an electric field between said nozzle and an accelerating electrode placed several millimeters ahead of the nozzle. The ink droplets are directed toward the surface of the printing paper by providing a strong electric field between the nozzle and the platen and further electrostatically deflected in both primary and secondary directions (right and left directions) to thereby print letters, signs, etc., on the surface of the paper.
There is also known a popularly employed system in which ions produced between the electrodes applied with a high voltage are passed through an ink mist so that they are deposited with ink particles, and then these ink particle-carrying ions are selectively adsorbed on the surface of the printing paper to thereby effect printing.
The device of the present invention pertains to the last-mentioned system, and so this system is first described in detail for facilitating better understanding of the present invention.
Referring to FIG. 1, reference numeral 101 denotes a paper on which printing is to be made (hereinafter referred to as printing paper), 102 a platen incorporated with a cathode 103, 104 a wire-shaped anode, and 105 an aperture board disposed in front of said anode 104 and consisting of a selecting electrode 105mist a common electrode 105b and an insulator 105c adapted to insulate said both electrodes from each other. This aperture board is provided in its surface with a plurality of apertures 105d arranged along the length of the board as shown in FIG. 2. Numeral 106 is an ink mist tank in which ink solution 107 is agitated by a plurality of vibrators 108 provided at the tank bottom so as to produce a mist of ink, 109 a main pump for feeding air both into the printing section and into said mist tank 106, and 110 a separator whereby the ink mist 112 recovered from the printing section 111 is separated into ink and air.
According to this system, ions are produced from the anode 104 and moved in the direction of the printing paper 101 by the action of an electric field formed between said anode 104 and cathode 103. In moving toward the printing paper, said ions pass through the apertures 105d in the aperture board 105, but their passage is either promoted or retarded as they receive the action of the electric field formed between the selecting electrode 105a and the common electrode 105b. Ion movement is promoted when the ions pass through the apertures 105d which correspond to the dots to be printed, and when these ions reach the ink mist 112 in the printing section 111, they are loaded with ink particles and further migrate toward the cathode 103 while carrying such ink particles therewith and then are adsorbed on the surface of the printing paper 101 to effect printing by way of dots. In this way, letters, figures, etc., in the form of dots are printed on the printing paper, with the above-described operation being programmed as main scanning and feed of the printing paper as auxiliary scanning.
In such type of high speed printing apparatus, it is often experienced that the letters, etc., are printed too lightly. This is mostly due to shortage or deficiency of ink mist supplied to the printing section 111 from the mist tank 106. That is, as there exists a certain distance between the mist source and the mist delivery port, the ink particles tend to be diffused by the air supplied for carrying the ink mist in the mist tank 106 to the printing section 111, and also many small convections are formed in the mist tank, and these factors to reduce the amount of ink mist which is actually carried into the printing section by said air.